Aquaplaning: an investigation of surface flow calculation

Abstract

This research project will numerically analyse current methods used for calculating surface flow depth and the accuracy of different models. It will model the surface flow build up over the duration of a design storm event using the standards values which are determined from the following research and documentation.

This research project compares the accuracy and reliability of surface flow calculation methods including the Gallaway Equation, Manning’s Equation and a kinematic wave equation model. The research reviews current design rainfall intensity values as well as other input variables such as texture depth, acceptable flow depth and driver behaviour and determines if they are suitable for study of aquaplaning analysis.

Current standards outline procedure for choosing input variable based on the conditions. These have been based on historical studies and still seem applicable to today. A design rainfall intensity of the 1 year ARI, 5 minute duration or 50mm/h, whichever is the lesser, is chosen to account t for driver behaviour and time of concentration. The standard texture depth should be chosen depending on the specified pavement type or determined by on site testing if available.

The Gallaway equation provides a fast a simple method to calculate depth however in areas of particular concern or risk a more extensive hydraulic analysis with the use of the kinematic wave equations may be warranted. The RRL method produce high depths of flow and is therefore no recommended for use in Australia.

This research investigates the time of concentration and surface drainage of the flow path to assess the aquaplaning risk over time. The results suggest the maximum flow depth conditions will be reached for surface drainage catchments after approximately 5 minutes and the depth will subside to below critical depth within 5 minutes of thecessation of the rainfall.